The invention relates to an internal combustion engine having an exhaust-gas turbocharger with an exhaust turbine and a valve arranged in the exhaust gas duct upstream of the turbine of the turbocharger for releasing exhaust gas from the exhaust gas duct.
The document DE 198 57 234 A1 describes a turbocharged internal combustion engine whose exhaust-gas turbine is equipped with variable turbine inlet guide vanes for controlling the effective inlet flow cross-section of the turbine. The turbine guide vane structure can be inserted axially into the inlet flow passages of the turbine and is used, in particular in the engine braking mode, to reduce the inlet flow cross section of the turbine. As a result, the exhaust-gas back pressure is increased and the pistons in the cylinders of the internal combustion engine have to perform exhaust work against the increased exhaust gas pressure. As a result, the engine braking performance can be considerably increased. In the engine operating mode, in contrast, the guide vane structure is under full load fully withdrawn from the inlet flow passages of the turbine, in order to provide for maximum exhaust-gas mass flow through the turbine.
In order to avoid impermissibly high loading of components both at maximum power operation of the engine and in the engine braking mode and to achieve controlled operation, for example in order to implement a cruise control function, a bypass which bridges the turbine and has an adjustable bypass valve is provided, the bypass branching off from the exhaust pipe upstream of the turbine and extending to the exhaust-gas duct downstream of the turbine. Since considerably higher exhaust-gas back pressures occur in the engine braking mode than in the driving mode, mass flows of the exhaust gas via the bypass of differing magnitude are diverted with the same opening state of the bypass valve. This has to be taken into consideration by different control strategies for release of exhaust gas via the bypass.
It is the object of the invention to provide a charged internal combustion engine wherein the exhaust-gas mass flow, which is to be released so as to bypass the exhaust-gas turbine, is controlled by simple measures, both in the engine braking mode and in the engine driving mode.